1. Field of the Invention
The present invention relates to a communication system, and more particularly, to an error detection code generating method and an error detection code generator in a mobile communication system.
2. Background of the Related Art
Typically, radio communication systems for transferring packet data use physical channels, such as, Packet Data Channel (hereinafter referred to as PDCH), Packet Data Control Channel (hereinafter referred to as PDCCH) and so forth.
The PDCH is a channel for use of transferring packet data that actually needs to be transferred to a relevant terminal, mobile station or user (hereinafter being used interchangeably). Many users prefer the PDCH based on the Time Division Multiplexing system (hereinafter referred to as TDM system). The PDCCH contains control information, enabling a terminal to receive the data being transferred through the PDCH without error.
FIG. 1 illustrates a control message format and a number of information bits transmitted through PDCCH according to a related art for a TDM system. The ARQ (automatic request) channel identifier and subpacket identifier are binary information bits informing the terminal of whether information including PDCH corresponding to PDCCH is to be retransmitted or not. The encoder packet size is binary information bits informing a data information bit number transmitted on PDCH. The MAC identifier is a terminal identifier, and values except (000000)2 indicate that control information of PDCCH is transferred to which terminal.
When a base station transfers packet data using TDM system, or schedules data and later sending the data to each terminal in sequence, the packet data, which is transmitted to every terminal, always uses all of the available resources, e.g., Walsh codes, in the PDCH. Even when only a part of the available resources needs to be used, all of the resources are still used for the packet data. As a result thereof, most of other resources are wasted at the same time.
For example, data sent on PDCH need to be coded and decoded based on Walsh codes. Serial bits are converted to parallel, and the parallel bits are coded using the Walsh codes. In order to decode the data, the information regarding the Walsh codes is sent on the PDCCH.
In TDM system, there are plurality of time intervals 1, 2, 3, 4, 5, 6, etc, and only one of a plurality of terminals is allotted for each time interval where a PDCH and PDCCH are sent to the terminal during this allotted time interval. For example, if there are users 1 and 3 and time intervals 1 and 3, respectively, and if all 32-ary Walsh codes are available for use by terminal 1, all 32-ary Walsh codes are utilized in the PDCH during time interval 1. However, if the available Walsh codes decrease in time interval 3, all decreased Walsh codes are utilized for the PDCH. Even before terminal 3 can use the changed/decreased Walsh codes in time interval 3, it needs to know this information. In order to achieve this, the BS broadcasts such information using a Walsh Code Space Identification Identifier (WSI) field in the PDCCH (without PDCH) with MAC_ID field information bit of (000000)2 before time interval 3 to all terminals within a cell. And, the base station explicitly transmits a control message including MAC_ID to the terminals on PDCCH.
A base station regularly or irregularly broadcasts WSI on the PDCCH without the PDCH to all terminals under its management. In the course of the broadcast, the base station uses every possible power for all terminals (even including terminals in the worst environment) to be able to receive the information such that even the terminals in the worst environment can receive the WSI. Hence, the broadcasting consumes much power. Moreover, when the WSI change, the base station has to inform the changes to all terminals every time. In those cases, the base station cannot transmit PDCH, so the transmission efficiency of the entire system is consequently reduced.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.